1. Field of the Invention
The present invention relates to a rotatable video camera, and, more particularly, to a communication system for transmitting data signals to remotely control a rotatable video camera, and for receiving video and data signals from a rotatable video camera, wherein the data and video signals may be modulated.
2. Description of the Related Art
There are numerous known video surveillance systems which may be used to monitor a given space or track a moving object such as a person or vehicle. Some such systems utilize fixed cameras having a stationary field of view (FOV). To fully cover a given surveillance site with a fixed camera system, however, it will oftentimes be necessary to use a significant number of fixed cameras.
Movable cameras which may pan, tilt and/or zoom are also known. Panning involves rotating the camera about a substantially vertical axis of rotation. Tilting involves rotating the camera about a substantially horizontal axis of rotation. Zooming involves adjusting the focal length of the camera, such as by modifying the distances between lens elements. The use of a PTZ (pan, tilt, zoom) camera system will typically reduce the number of cameras required for a given surveillance site and also thereby reduce the number and cost of the video feeds and system integration hardware such as multiplexers and switchers associated therewith. Another advantage of PTZ camera systems is that they can be controlled to automatically focus upon and follow a target of interest without operator intervention. Real-time video content analysis can be used to control the panning, tilting and zooming of a camera such that a target is acquired and followed automatically. The real-time video content analysis can be performed either remotely, or locally in the system controller processor of the camera.
Control signals for directing the pan, tilt, zoom movements typically originate from a human operator via a joystick or from an automated video tracking or surveillance system. The control signals are generally transmitted from a stationary portion of the system to the movable camera. Of the three common types of camera movement, panning, tilting and zooming, it is generally desirable to allow the camera to have an unlimited or continuous range panning motion, while tilting and zooming typically involve motion that is restricted within a range having two end points. Wires or flex circuit connections can be used in applications where panning is restricted within a range having two end points. However, the use of slip rings may be necessary to provide the camera with continuous panning motion. It is also common to mount a PTZ camera such that the panning interface occurs between a stationary base and camera assembly. In contrast, the tilting motion of the camera typically occurs between two portions of the camera assembly which are both being rotated relative to the panning axis.
Various assemblies have been developed to provide electrical communication across the panning interface between the stationary portion of the system and the moveable camera assembly that will allow the indefinite or continual rotation of the camera assembly about the panning axis. For example, slip rings may be used to provide electrical communication across a rotational interface without restricting the range of such rotation. Known slip rings include drum style and platter style slip rings. Such slip rings rely upon sliding engagement between electrical contacts to provide electrical communication. One drawback of such slip rings is that the sliding contacts are inherently noisy in an electrical sense. The slidable contacts of a slip ring are also subject to wear which may result in a loss of electrical contact or degradation of the electrical connection provided by the contact which exacerbates the electrical noise problem.
It is also known to use a light emitting device and a light sensitive device both of which are positioned on the panning axis to transmit signals across the panning interface in a single direction.
It would be desirable in the art to provide an improved camera system that allows the camera to pan indefinitely without losing communication with a stationary base, and that allows bi-directional communication between the camera and the stationary base without a high level of electrical noise.